The invention relates to an electrical circuit arrangement for converting an input voltage into an impressed electrical output variable, there being a predetermined assignment between input voltage and output variable.
A circuit arrangement of this type is disclosed in DE 195 47 155 C1. It is provided in particular as a desired value transmitter for driving continuous hydraulic valves with integrated drive electronics. The known circuit arrangement converts an electrical input voltage into an impressed electrical output variable. There is a linear relationship between the input voltage and the output variable. If the load resistance connected to the circuit arrangement is smaller than a predetermined value of e.g. 500 xcexa9, the input voltage is converted into an output current. By contrast, if the load resistance is greater than the predetermined value, the input voltage is converted into an output voltage. The fact of whether the electrical output variable is a voltage or a current depends on the magnitude of the load resistance. With this circuit arrangement, it is not possible to convert the input voltage into an output current or into an output voltage independently of the magnitude of the load resistance.
The invention is based on the object of providing an electrical circuit arrangement of the type mentioned in the introduction which converts an input voltage, fed to the circuit arrangement, optionally into an output current or into an output voltage independently of the magnitude of the load resistance.
According to the invention the input voltage (ue) is fed to a desired value input (5) of a regulator (4), a negative feedback voltage (ug) is fed to an actual value input (6) of the regulator (4), said negative feedback voltage being a measure of the respectively effective output variable (ua, ia) of the circuit arrangement, for converting the input voltage (ue) into an output voltage (ua), the negative feedback voltage (ugu) is a voltage (k1xc3x97ua) proportional to the output voltage (ua), and for converting the input voltage (ue) into an output current (ia), the negative feedback voltage (ugi) is a voltage (k2xc3x97Au) which is proportional to a voltage (xcex94u=iaxc3x97R8) dropped across a first resistor (8) through which the output current (ia) flows. The invention makes it possible to convert an input voltage optionally into an output voltage or into an output current in a manner dependent on a control signal fed to the circuit arrangement. When the input voltage is converted into an output voltage, it is possible to realize different values of the gain factor between input voltage and output voltage. Equally, when the input voltage is converted into an output current, it is possible to realize different values of the gain factor between input voltage and output current.
Through additive superposition of a constant voltage to the voltage which is a measure of the output voltage of the circuit arrangement, the output voltage range can be shifted relative to the input voltage range. In particular, a unipolar input voltage whose range extends e.g. from 0 V to xe2x88x925 V can be converted into a bipolar output voltage whose range lies e.g. between xe2x88x9210 V and +10 V. Computing circuits are preferably provided for forming the negative feedback voltages. The use of electronic analog switches formed as changeover switches allows driving of the changeover switches with low-power electrical control signals. Electronic switches require little space. They have a low susceptibility to interference since they contain no mechanical contacts which can wear over the course of time or exhibit contact resistances. In contrast to electromagnetic relays, the power loss which occurs when the coil of a relay is energized and the associated evolution of heat are obviated in the case of electronic switches. A constant voltage which is additionally fed to the second computing circuit ensures that even when the input voltage is converted into an output voltage, positive voltage values are present at the inputs of the electronic switch. Advantageous configurations of the regulator and of the computing circuits are specified. A power amplifier arranged between the output of the regulator and the resistor through which the output current flows makes it possible to manage with a lower supply voltage than if an operational amplifier with a correspondingly large output current is used in the regulator.